Sub-micron resolution depth profiling of thin coatings using step-scan photoacoustic FT-IR spectroscopy

摘要

Recent advances in photoacoustic FT-IR spectroscopy have generated considerable interest in the application of this technique in the area of depth profiling characterizations of heterogeneous samples. One category of such samples involves systems having few micron thin layered structures coated on relatively thick polyester substrates. In particular, step-scan interferometry offers several specific advantages such as constant thermal diffusion depth, sensitivity even at short wavelengths and easy retrieval of the signal phase. The phase delay of the photoacoustic signal is used in conjunction with the knowledge of the thermal properties of the coated fluids in the calculation of the relative as well as the absolute depths of these multi-layered coatings. The phase delay is calculated at wavelengths that are characteristic of the various components of the different layers in the system.